ntfs3: pretend $Extend records as regular files

Since commit af153bb63a33 ("vfs: catch invalid modes in may_open()")
requires any inode be one of S_IFDIR/S_IFLNK/S_IFREG/S_IFCHR/S_IFBLK/
S_IFIFO/S_IFSOCK type, use S_IFREG for $Extend records.

Reported-by: syzbot <[e-mail]>
Closes: https://syzkaller.appspot.com/bug?extid=895c23f6917da440ed0d
Signed-off-by: Tetsuo Handa <[e-mail]>
Signed-off-by: Konstantin Komarov <[e-mail]>

fs/ntfs3/inode.c

···
 		   fname->home.seq == cpu_to_le16(MFT_REC_EXTEND)) {
 		/* Records in $Extend are not a files or general directories. */
 		inode->i_op = &ntfs_file_inode_operations;
+		mode = S_IFREG;
 	} else {
 		err = -EINVAL;
 		goto out;